1. Field of the Invention
The invention relates to a frictional hinge device which is used to pivotably support a lid plate and a display of a portable business device such as a laptop note type personal computer, and particularly concerns to a frictional hinge device used to hold the lid plate and the display at a desired angular position by friction.
2. Description of Prior Art
In this type of the frictional hinge device, a lid plate is secured to a metallic shaft which is rotatably supported on a holder block metal. The holder block metal clamps the metallic shaft to produce a surface friction between the holder block metal and the metallic shaft so as to hold the lid plate at a desired angular position.
Although this makes a whole structure simple and contributes to cost reduction, a certain quantity of grease is required for lubrication between the holder block metal and the metallic shaft. The grease becomes a likely cause of perimetric pollution around the frictional hinge device.
In order to avoid these inconveniences, a shaft lock device is disclosed by Laid-open Japanese Patent Application No. 7-26825 (laid-open on Jan. 27, 1995, assigned to Kabushiki Kaisha Kato Manufacturing Factory). This teaches that an outer shaft is made of a synthetic resin and integrally molded with an inner shaft. Due to a surface friction resistance caused from a thermal expansional difference between the inner and outer shafts, it is possible to hold the inner shaft at a desired angular position while permitting the inner shaft to pivot relative to the outer shaft against the surface friction resistance therebetween. This surface friction resistance holds a display of a note type personal computer at the desired angular position.
In the shaft lock device disclosed by the Laid-open Japanese Patent Application No. 7-26825, a surface roughness, surface treatment and frictional coefficient are suggested as means to determine the frictional torque between the inner and outer shafts together with their diametrical dimensions.
However, this disclosure remains silent about qualitative and quantitative analyses on a relationship between the inner and outer shafts. This causes no smaller variations on the frictional torque when the inner shaft pivotally moves in relative to the outer shaft. This also causes abnormal noise due to a stickslip phenomenon when pivotally moving the inner shaft, thereby losing a good endurance with the frictional torque reduced due to an unacceptable amount of wear between the inner and outer shafts.
Therefore, the present invention has been made with the above drawbacks in mind, it is a main object of the invention to provide a frictional hinge device which is inexpensive with no fear for perimetric pollution and no abnormal noise due to a stickslip phenomenon with the least torque variations and is capable of maintaining a stable surface friction resistance between a shaft member and a support member for an extended period of time so as to repeatedly hold the support member at a desired angular position based on the surface friction resistance.
With a frictional hinge device having a support member rotatably supported by a metallic shaft member, a support member is integrally molded around the metallic shaft member when a synthetic resin is injected into a mold cast in which the metallic shaft member is placed beforehand.
The synthetic resin is contracted when solidified, the support member tightly engages with the metallic shaft member. Due to selection of materials or provision of a surface treatment, an outer surface of the metallic shaft member has Vickers number (Hv) of 800 or more. This provides a good surface friction resistance therebetween. When the support member is subjected to a frictional torque greater than the surface friction resistance, the support member pivots around the metallic shaft member relatively. When the support member is subjected to a frictional torque less than the surface friction resistance, the support member is held at an appropriate angular position by the surface friction resistance.
With the synthetic resin molded around the metallic shaft member, it is possible to reduce a manufacturing cost.
With the outer surface of the metallic shaft member treated so that it has Vickers number (Hv) of 800 or more, it is possible to hold e.g., 30000 times of opening and closure operations with the least wear between the metallic shaft member and the support member. This insures a long service life because a torque holding rate (%) is improved {(i.e., torque measured after undergoing a heat deteriorating experimental test or endurance experimental test)/(initial torque)}xc3x97100. This also reduces frictional torque variations and a stickslip phenomenon significantly with no abnormal noise due to the stickslip phenomenon when the support member pivots in relative to the metallic shaft member. With the invariable surface friction resistance thus maintained substantially, it is possible to readily hold the support member at a desired angular position, and securing a stable surface friction resistance for an extended period of time with a good durability.
With the synthetic resin molded around the metallic shaft member to produce the surface friction resistance, the need of applying the grease is eliminated to dissolve the fear for perimetric pollution.
With a hardened layer provided around an outer surface of the metallic shaft member, the torque holding rate is improved. By determining the hardened layer at least 5.0 xcexcm in thickness, the stable surface friction resistance is maintained between the support member and the metallic shaft member for an extended period of time.
Since an alteration of Vickers number (Hv) leads to appropriately adjusting the surface friction resistance between the support member and the metallic shaft member, a necessary surface friction resistance is readily selected as desired in accordance with types of the frictional hinge devices.
With one or more circumferential grooves provided on the outer surface of the metallic shaft member, the support member tends to engage more tightly against the metallic shaft member so that the surface friction resistance is reinforced between the support member and the metallic shaft member so as to insure an enhanced frictional torque therebetween. This makes the frictional hinge device compact as a whole in comparison with a higher frictional torque insured.
With the frictional hinge device used to pivotably move a display for a portable business device, it is possible to hold the display at any desired angular position to insure a good view on the display.
With the synthetic resin applied to the support member in which a bending elasticity fluctuates as small as up to 30% under an operating temperature ranging from e. g., xe2x88x9220 to 80xc2x0 C., it is possible to maintain a sufficient surface friction resistance against the metallic shaft member even when the normal ambient temperature fluctuates. This prevents deterioration of friction surfaces of the support member and the metallic shaft member so as to maintain the stable surface friction resistance for an extended period of time.
By way of illustration, the synthetic resin is represented by PC (polycarbonate), PAR (polyarylate), PPS (polyphenylene sulphide) and the like.
With the synthetic resin mixed with an organic or inorganic antifriction medium, it is possible to impart a smooth pivotal movement with the shaft member. As opposed to the case in which lubrication agent is applied between the support member and the shaft member, it is possible to prevent the perimeter from being polluted. Due to a difference of hardness between the support member and the metallic shaft member, it is possible to exceedingly reduce the wear dust produced between the support member and the shaft member, thereby maintaining the stable surface friction resistance therebetween for an extended period of time.
By mixing the synthetic resin with fibrous material to improve its mechanical strength, it is possible to ameliorate an endurance of the support member.